The present invention relates to an FRP molded article and a production process thereof.
The FRP molded article of the invention comprises a thermoplastic resin used as a matrix resin and reinforcing fibers having an average fiber length of 0.1 to 7 mm dispersed in the matrix resin. The FRP molded article is thin-walled and has excellent mechanical properties and low volume resistivity. It can be preferably used as a housing of an electronic terminal machine or device, portable cellular phone, etc.
The molded article of the invention can be produced by a hot-runner injection molding method.
Injection-molded articles made from synthetic resins are widely used, for example, as structural parts such as functional parts and mechanical parts, and housings of office machines and devices, electronic terminal machines and devices, portable cellular phones, etc. Especially the injection-molded articles made from carbon fiber-reinforced resins are widely used as housings of computer terminal machines and apparatuses, portable cellular phones, etc., since they have excellent mechanical properties and high electromagnetic wave shielding capability.
Molded thermoplastic resin articles are mostly produced by injection molding methods. When a desired injection molded article made from a thermoplastic resin is produced by an injection molding method, the portions called sprue runners to be thrown away after molding are formed in addition to the portion destined to be a product. Usually the rate by weight of the sprue runners to the molded article is small, and the shapes of the sprue runners do not pose any large problem.
However, in the case where a molded article reinforced by carbon fibers or other reinforcing fibers is produced by an injection molding method, especially in the case where a complicatedly shaped large-sized molded article like a housing of a terminal machine or device of a personal computer is produced by an injection molding method, a molten resin composed of a mixture of a thermoplastic resin and reinforcing fibers is poor in flowability. Therefore, multi-gate molding, in which many gates are used for injecting the molten resin, is employed. In this case, the rate by weight of a sprue runner portion in a molded article thereto becomes large and as a result material to be thrown away increases.
A thermoplastic resin reinforced by reinforcing fibers is high in the unit cost of material compared with general engineering plastics. Therefore, in the conventional molding methods, in which the number of sprue runners to be thrown away is large, the cost of the molded article is inevitably higher.
If sprue runners exist, flow resistance acts on the molten resin flowing there, to break and thin the reinforcing fibers contained in the molten resin. As a result, the physical properties of the obtained molded article decline.
Injection molding using hot runners is already practically used for molding of thermoplastic engineering plastics not containing reinforcing fibers.
On the other hand, several cases are known, in which a thermoplastic resin containing reinforcing fibers is molded by means of injection molding using hot runners. However, no attempt is known, in which a thermoplastic resin containing carbon fibers as reinforcing fibers is molded by means of injection molding using hot runners.
One reason is that in the case where a thermoplastic resin reinforced by reinforcing fibers is molded by means of hot-runner injection molding, it is feared that the product becomes poor in appearance and is warped. As another reason, since no means for technically overcoming the feared defects has been examined, molded article manufacturers consider that there is a risk in employing the technique for producing sellable molded articles.
An object of the invention is to greatly reduce sprue runners that raise the cost of the injection-molded article made from a highly functional material, i.e., a thermoplastic resin reinforced by reinforcing fibers, and another object is to provide an injection molded article made from a thermoplastic resin reinforced by reinforcing fibers, which is substantially free from defects such as poor appearance and warping.
The FRP molded article of the invention to achieve the above-mentioned objects is as follows:
An FRP molded article comprising a thermoplastic resin and resin-reinforcing fibers having an average fiber length of 0.1 to 7 mm dispersed in said thermoplastic resin, produced by a hot-runner injection molding.
In the FRP molded article of the invention, it is preferable that the fibers are at least one kind of fibers selected from a group consisting of carbon fibers, glass fibers and aramid fibers.
In the FRP molded article of the invention, it is preferable that the length of the hot-runner sprue used in the hot-runner injection molding is 10 to 600 mm.
In the FRP molded article of the invention, it is preferable that the depression formed by the tip of a gate pin used for opening and closing a gate provided at the tip of the hot-runner sprue exists on the surface of the molded article.
In the FRP molded article of the invention, it is preferable that the depression has a diameter of 0.1 to 10 mm and a depth of 2 mm or less.
In the FRP molded article of the invention, it is preferable that the hot-runner injection molding has plural hot-runner sprues having opening-closing gates at the tips thereof respectively and each of the opening-closing gates is controlled independently each other.
In the FRP molded article of the invention, it is preferable that the hot-runner sprue comprises plural hot-runner sprues and a resin passing through a first sprue of an injection molding machine communicating to the plural hot-runner sprues passes through respective resin passages and is injected from the respective gates provided at the tips of the respective hot-runner sprues substantially at the same timing.
In the FRP molded article of the invention, it is preferable that the geometrical lengths of the respective resin passages are equal to each other.
In the FRP molded article of the invention, it is preferable that there are time differences in the opening and closing timings of the respective gates.
In the FRP molded article of the invention, it is preferable that the molded article is an equipment body.
The process for producing the FRP molded article of the invention for achieving the above-mentioned objects is as follows:
A process for producing an FRP molded article, comprising:
(a) a first step, in which resin pellets having resin-reinforcing fibers having an average fiber length of 0.1 to 7 mm mixed in a thermoplastic resin used as a matrix resin are heated and molten at 220 to 350xc2x0 C. in a resin-melting cylinder of an injection molding machine, to prepare a molten resin having the fibers dispersed therein, and
(b) a second step, in which the molten resin obtained in the first step is fed to a hot-runner sprue through a first sprue of the injection molding machine and further through the resin passage of a hot-runner injection molding apparatus; the gate of the hot-runner sprue is opened and closed to control the start and end of injection of the molten resin into a cavity of a mold used for molding an article; the molten resin fed into the cavity is solidified in the mold; the mold is opened; and the molded article is taken out.
In the process for producing an FRP molded article of the invention, it is preferred that the length of the hot-runner sprue is 10 to 600 mm.
In the process for producing an FRP molded article of the invention, it is preferred that the gate is opened and closed by a gate pin going into and out of the gate, and that a depression is formed on the surface of the molded article by the tip of the gate pin.
In the process for producing an FRP molded article of the invention, it is preferred that the depression has a diameter of 0.1 to 10 mm and a depth of 2 mm or less.
In the process for producing an FRP molded article of the invention, it is preferred that the hot-runner sprue comprises plural hot-runner sprues and the opening and closing of the respective gates provided at the tips of the plural hot-runner sprues can be controlled respectively independently.
In the process for producing an FRP molded article of the invention, it is preferred that the hot-runner sprue comprises plural hot-runner sprues, and the resin passing through a first sprue of an injection molding machine communicating to the plural hot-runner sprues passes through respective resin passages and is injected from the respective gates at the tips of the respective hot-runner sprues at the same timing.
In the process for producing an FRP molded article of the invention, it is preferred that the geometrical lengths of the respective resin passages are equal to each other.
In the process for producing an FRP molded article of the invention, it is preferred that there are time differences in the opening and closing timings of the respective gates.